Method and computer program product to improve I/O performance and control I/O latency in a redundant array

Abstract

A method and computer program product for improving I / O performance and controlling I / O latency for reading or writing to a disk in a redundant array, comprising determining an optimal number of I / O sort queues, their depth and a latency control number, directing incoming I / Os to a second sort queue if the queue depth or latency control number for the first queue is exceeded, directing incoming I / Os to a FIFO queue if all sort queues are saturated and issuing I / Os to a disk in the redundant array from the sort queue having the foremost I / Os.

Description

FIELD OF THE INVENTION [0001] The disclosed invention relates to RAID controllers and more specifically to improving I / O performance and controlling I / O latency for a RAID array. BACKGROUND OF INVENTION [0002] There are many applications, particularly in a business environment, where there are needs beyond what can be fulfilled by a single hard disk, regardless of its size, performance or quality level. Many businesses can't afford to have their systems go down for even an hour in the event of a disk failure. They need large storage subsystems with capacities in the terabytes. And they want to be able to insulate themselves from hardware failures to any extent possible. Some people working with multimedia files need fast data transfer exceeding what current drives can deliver, without spending a fortune on specialty drives. These situations require that the traditional “one hard disk per system” model be set aside and a new system employed. This technique is called Redundant Arrays ...

AI Technical Summary

Benefits of technology

[0012] The invention comprises a method and computer program product for improving I/O performance and controlling I/O latency for reading or writing to a disk in a redundant array, comprising determining an optimal number of I/O sort queues, their depth and a latency control number, di...

Problems solved by technology

Many businesses can't afford to have their systems go down for even an hour in the event of a disk failure.

While this does reduce movement of the disk's head, it is however an “unfair algorithm” in that it will continuously sort new I / Os ahead of previously received I / Os if the read or write location for the new I / Os precedes that of the previously received I / Os.

However, if the incoming I / O rate is high, then possibly an excessive number of new I / Os are sorted before previously received I / Os, thereby creating an unfair algorithm.

However, the tradeoff is excessive disk head movement which results in increased I / O latency.

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